Cooling system for nozzle segment platform edges

Abstract

The cooling system for the nozzle edges includes a chamber containing a cooling medium. First and second elongated plenums are disposed along opposite side edges of each platform. Inlet passages communicate cooling medium from the chamber into each plenum. Outlet passages from each plenum terminate in outlet holes in the side edges of the platform to cool the gap between adjacent nozzle segments. Passageways communicate with each plenum and terminate in film cooling holes to film cool platform surfaces. In each plenum, the inlet passages are not in direct line-of-sight flow communication with the outlet passages and passageways.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates generally to a cooling system for the nozzle segments of a gas turbine and particularly relates to a cooling system for cooling the adjoining edges of inner and outer platforms of adjacent nozzle segments arranged in an annular array about the axis of the turbine. [0002] In gas turbines, annular arrays of nozzles are disposed in the hot gas path for turning and accelerating the gas flow for optimum performance of the buckets. In the first stage of a turbine, for example, there are a plurality of circumferentially spaced nozzle vanes which extend generally radially between inner and outer annular bands which serve to confine the gas flow to an annular configuration as the gas flows through the multiple stages of the turbine. A plurality of circumferentially spaced buckets mounted on the turbine rotor lie axially downstream of the annular array of nozzles and form a turbine stage with the nozzles. The nozzles, for exampl...

AI Technical Summary

Benefits of technology

"The present invention provides a cooling system for a turbine nozzle segment that includes inner and outer platforms and a vane extending therebetween. The cooling system includes a source of cooling medium, elongated plenums, inlet and outlet passages, and film cooling holes. The invention is designed to provide continuous cooling along the edges of the platforms in the hot gas path through the use of a cooling medium that flows through the plenums and film cooling holes. The cooling system is arranged such that the inlet and outlet passages do not have direct line-of-sight flow of the cooling medium, which leads to improved cooling efficiency and a more uniform cooling effect."

Problems solved by technology

Film cooling from an adjacent nozzle to cool the platform edge, however, causes a debiting of the cooling effectiveness when the cooling film crosses the nozzle intersegment gap.

When long holes running from an impingement cavity are utilized, the convective cooling of the edge by the holes is discrete rather than continuous and, therefore, less efficient.

Perfect alignment of the adjoining edges of the nozzle segments, however, is difficult to achieve and maintain as a result of manufacturing and thermomechanical problems.

A boundary layer trip at the adjoining edges of the platforms results in a spike in heat transfer near the edge of the platform and also results in a debit to the cooling effectiveness of any film cooling medium that crosses the gap.

Thus, the edges of nozzles segment platforms which extend generally parallel to the turbine axis are subject to severe thermal distress due to boundary layer trip.

Images